Dispersing and softening agent for positive electrode of lithium iron phosphate battery, preparation method of dispersing and softening agent, positive electrode slurry of lithium iron phosphate battery and positive electrode piece prepared from positive electrode slurry

Abstract

The invention relates to the technical field of lithium battery materials, in particular to a dispersing and softening agent for a lithium iron phosphate battery positive electrode, a preparation method of the dispersing and softening agent, lithium iron phosphate battery positive electrode slurry containing the dispersing and softening agent, and a positive electrode piece prepared from the positive electrode slurry. The dispersing and softening agent is formed by polymerizing a phosphate monomer, an amine monomer, an amide monomer and an ether monomer. The dispersing and softening agent solves the problems of single function of a dispersing agent and a softening agent, poor slurry performance, insufficient flexibility of a pole piece and the like in the prior art.

Description

Technical Field

[0001] This invention relates to the field of lithium battery materials technology, specifically to a dispersant and softening agent for the positive electrode of a lithium iron phosphate battery and its preparation method, a lithium iron phosphate battery positive electrode slurry containing the dispersant and softening agent, and a positive electrode sheet prepared from the positive electrode slurry. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are widely used in new energy vehicles, energy storage devices, and other fields due to their advantages such as high safety, long cycle life, and low cost. As the core component of LFP batteries, the performance of the cathode material directly affects the overall battery performance. In the preparation of the LFP battery cathode, the dispersion stability, solid content, and filterability of the cathode slurry, as well as the flexibility and elongation of the cathode sheet, are key process indicators that significantly impact the battery's processing performance and final performance.

[0003] Currently, most commonly used cathode slurry dispersants in existing technologies are single-type polymers, such as polyacrylic acid and polyether. While these dispersants can improve the dispersibility of the slurry to some extent, they cannot simultaneously meet the requirements of increasing solids content, maintaining viscosity stability, and optimizing filterability. Meanwhile, existing flexibility agents are mostly esters or waxes, which have poor compatibility with cathode slurries. Their addition can easily lead to a decrease in slurry stability, and their effect on improving electrode flexibility is limited, making it difficult to effectively reduce electrode elongation and affecting the cycle stability and safety of the battery.

[0004] Therefore, developing a dispersant that can simultaneously improve the solid content, viscosity stability, and filterability of the cathode slurry, as well as enhance the flexibility of the cathode sheet and reduce the elongation of the sheet, is of great significance for promoting the performance optimization of lithium iron phosphate batteries. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a dispersant and flexible agent for the positive electrode of lithium iron phosphate batteries and its preparation method. It also provides a lithium iron phosphate battery positive electrode slurry containing the dispersant and flexible agent and a positive electrode sheet prepared from the slurry, thus solving the problems of single function of dispersants and flexible agents, poor slurry performance, and insufficient electrode sheet flexibility in existing technologies.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a dispersant and softening agent for the positive electrode of a lithium iron phosphate battery, characterized in that the dispersant and softening agent is polymerized from phosphate ester monomers, amine monomers, amide monomers and ether monomers; The general molecular structure of the dispersant and softening agent is shown in formula (I): ; Wherein, R¹ is H or a C1~C4 alkyl group; R² is a C1~C3 alkyl group or a C1~C3 amino-substituted alkyl group; R³ is H or a C1~C3 alkyl group; n is an integer from 1 to 5; m is an integer from 3 to 10; and k is an integer from 50 to 200.

[0007] Preferably, the phosphate monomer is selected from one or more of phosphate methacrylate, phosphate ethyl acrylate, and allyl dihydrophosphate.

[0008] Preferably, the amine monomer is selected from one or more of diethanolamine acrylate, N-methyldiethanolamine methacrylate and aminoethyl methacrylate.

[0009] Preferably, the amide monomer is selected from one or more of acrylamide, methacrylamide, and N-methacrylamide.

[0010] Preferably, the ether monomer is selected from one or more of polyethylene glycol monomethyl ether acrylate, polyethylene glycol monoethyl ether methacrylate, and polypropylene glycol monomethyl ether acrylate.

[0011] Preferably, the molar ratio of the phosphate ester monomer, amine monomer, amide monomer and ether monomer is 20~35:15~25:10~20:25~40.

[0012] Secondly, the present invention provides a method for preparing a dispersant and softening agent as described in the present invention, the method comprising: adding phosphate ester monomers, amine monomers, amide monomers and ether monomers in the presence of a solvent, adding an initiator, and carrying out a polymerization reaction under an inert atmosphere; Alternatively, in the presence of a solvent, the main chain backbone monomers are prepolymerized first, then the remaining branched monomers are added and mixed, an initiator is added, and the polymerization reaction is carried out under an inert atmosphere. The main chain backbone monomer is selected from two of the following: phosphate ester monomers, amine monomers, amide monomers, and ether monomers; The remaining branched monomers are monomers other than the main chain backbone monomers among phosphate ester monomers, amine monomers, amide monomers, and ether monomers.

[0013] Preferably, the solvent is selected from one or more of N-methylpyrrolidone, dimethylformamide, and ethyl acetate.

[0014] Preferably, the phosphate monomer is selected from one or more of phosphate methacrylate, phosphate ethyl acrylate, and allyl dihydrophosphate.

[0015] Preferably, the amine monomer is selected from one or more of diethanolamine acrylate, N-methyldiethanolamine methacrylate and aminoethyl methacrylate.

[0016] Preferably, the amide monomer is selected from one or more of acrylamide, methacrylamide, and N-methacrylamide.

[0017] Preferably, the ether monomer is selected from one or more of polyethylene glycol monomethyl ether acrylate, polyethylene glycol monoethyl ether methacrylate, and polypropylene glycol monomethyl ether acrylate.

[0018] Preferably, the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and benzoyl peroxide.

[0019] Preferably, the inert atmosphere is a nitrogen atmosphere and / or an argon atmosphere.

[0020] Preferably, the molar ratio of the phosphate ester monomer, amine monomer, amide monomer and ether monomer is 20~35:15~25:10~20:25~40.

[0021] Preferably, the amount of the initiator added is 0.5 to 2% of the total mass of the four monomers: phosphate ester monomers, amine monomers, amide monomers, and ether monomers.

[0022] Preferably, the conditions for the polymerization reaction include: a temperature of 60~80℃, a stirring rate of 200~400rpm, and a time of 4~8h.

[0023] Preferably, the prepolymerization method includes: mixing monomers that serve as the backbone in the presence of a solvent, and carrying out a prepolymerization reaction at a temperature of 40-60°C, a stirring rate of 100-200 rpm, and a time of 1-2 hours.

[0024] Thirdly, the present invention provides an application of the dispersant and softening agent as described in the present invention in the positive electrode of a lithium iron phosphate battery, wherein the amount of the dispersant and softening agent added is 0.05 to 0.5% of the mass of the positive electrode active material, lithium iron phosphate.

[0025] Fourthly, the present invention provides a lithium iron phosphate battery positive electrode slurry, wherein the lithium iron phosphate battery positive electrode slurry is composed of the following components in mass fractions: 90-98% lithium iron phosphate, 0.1-2% conductive agent, 1.2-2.4% binder, and 0.05-0.5% dispersant and softener; The dispersing and softening agent is the dispersing and softening agent described in this invention.

[0026] Preferably, the solid content of the lithium iron phosphate battery cathode slurry is 55-70%.

[0027] Preferably, the conductive agent is selected from one or more of acetylene black, Ketjen black, and carbon nanotubes.

[0028] Preferably, the adhesive is polyvinylidene fluoride and / or polytetrafluoroethylene.

[0029] Preferably, the solvent for the lithium iron phosphate battery cathode slurry is N-methylpyrrolidone.

[0030] Fifthly, the present invention provides a positive electrode sheet for a lithium iron phosphate battery, wherein the positive electrode sheet is prepared from the positive electrode slurry of the lithium iron phosphate battery described in the present invention; The bending radius of the positive electrode sheet of the lithium iron phosphate battery is ≤6mm, and the elongation is ≤1%.

[0031] In the above technical solution, the dispersant and softening agent for the positive electrode of lithium iron phosphate battery of the present invention integrates multiple functional groups such as phosphate ester group, amino group, amide bond and ether bond through the reasonable combination and copolymerization of four monomers, so as to realize the integration of dispersion and softening functions. The functional groups work together to significantly increase the solid content of the positive electrode slurry to 70%, effectively reduce the amount of solvent used and improve production efficiency.

[0032] Among them, phosphate ester groups inhibit the agglomeration of lithium iron phosphate particles, and amide bonds improve the compatibility of each component, making the slurry more uniformly dispersed. After coating, the active material and conductive agent of the electrode are more regularly distributed, reducing internal resistance and improving the rate performance of the battery. The flexible segments provided by ether monomers penetrate into the interior of the electrode, improving the microstructure and reducing the bending radius of the positive electrode to less than 6mm, effectively avoiding cracking and powdering problems during processing (rolling, cutting) and use. The electrode elongation is controlled within 1%, reducing the structural damage caused by volume changes of the electrode during battery cycling and improving the cycle stability and safety of the battery.

[0033] Adding the dispersant and softener of this invention to the positive electrode slurry allows it to work synergistically with other components to further optimize the slurry performance, thereby improving the flexibility of the positive electrode sheet. As the solid content of the slurry can be increased to 70%, the slurry filtration speed is improved, and problems such as uneven coating and screen clogging are less likely to occur during the coating process. The electrode sheet drying efficiency is also higher, making it compatible with existing industrial production processes and easy to promote and apply on a large scale.

[0034] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0035] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0036] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0037] In a first aspect, the present invention provides a dispersant and softening agent for the positive electrode of a lithium iron phosphate battery, characterized in that the dispersant and softening agent is polymerized from phosphate ester monomers, amine monomers, amide monomers and ether monomers; The general molecular structure of the dispersant and softening agent is shown in formula (I): ; Wherein, R¹ is H or a C1~C4 alkyl group; R² is a C1~C3 alkyl group or a C1~C3 amino-substituted alkyl group; R³ is H or a C1~C2 alkyl group; n is an integer from 1 to 5; m is an integer from 3 to 10; and k is an integer from 50 to 200.

[0038] The dispersant and softener of this invention overcomes the bottleneck of single-function additives by integrating multiple functional groups through copolymerization of four specific monomers, achieving a unified function of dispersion, stabilization, compatibility, and softening. It solves the problems of existing dispersants struggling to balance solids content and viscosity stability, and the poor compatibility of softeners. After addition, the solids content of the slurry is significantly increased, and viscosity changes are more stable.

[0039] In this invention, the phosphate groups in the phosphate ester monomer molecules can form a strong interaction with the surface of the lithium iron phosphate cathode material, effectively preventing particle agglomeration and improving the dispersion effect. Specifically, they can be selected from one or more of phosphate methacrylate, phosphate ethyl acrylate, and allyl dihydrophosphate.

[0040] In this invention, the amine group in the amine monomer can regulate the interfacial charge distribution of the slurry, enhance the viscosity stability of the slurry, and facilitate uniform coating in the subsequent process. Specifically, it can be selected from one or more of diethanolamine acrylate, N-methyldiethanolamine methacrylate and aminoethyl methacrylate.

[0041] In this invention, the amide bond in the amide monomer can enhance the polarity and compatibility of the molecular chain, improve the filterability of the slurry, thereby accelerating the production speed of the electrode and improving production efficiency. Specifically, it can be selected from one or more of acrylamide, methacrylamide and N-methacrylamide.

[0042] In this invention, the flexible segments of the ether bonds in the ether monomer can improve the flexibility of the electrode, reduce the elongation of the electrode, and effectively avoid cracking and powder shedding during electrode processing (rolling, cutting) and use; and reduce structural damage to the electrode caused by volume changes during battery cycling, thereby improving battery cycle stability and safety. Specifically, it can be selected from one or more of polyethylene glycol monomethyl ether acrylate, polyethylene glycol monoethyl ether methacrylate, and polypropylene glycol monomethyl ether acrylate.

[0043] In this invention, the molar ratio of the phosphate ester monomers, amine monomers, amide monomers, and ether monomers is 20~35:15~25:10~20:25~40. This ratio range ensures the synergistic effect of each functional group, achieving the best dispersion and flexibility effect. The proportion of phosphate ester monomers in this invention maintains the flexibility of the electrode while preventing slurry agglomeration; the proportion of ether monomers in this invention ensures good dispersion stability of the slurry while guaranteeing the flexibility of the electrode.

[0044] Secondly, the present invention provides a method for preparing a dispersant and softening agent as described in the present invention, the method comprising: adding phosphate ester monomers, amine monomers, amide monomers and ether monomers in the presence of a solvent, adding an initiator, and carrying out a polymerization reaction under an inert atmosphere; Alternatively, in the presence of a solvent, the main chain backbone monomers are prepolymerized first, then the remaining branched monomers are added and mixed, an initiator is added, and the polymerization reaction is carried out under an inert atmosphere. The main chain backbone monomer is selected from two of the following: phosphate ester monomers, amine monomers, amide monomers, and ether monomers; The remaining branched monomers are monomers other than the main chain backbone monomers among phosphate ester monomers, amine monomers, amide monomers, and ether monomers.

[0045] The method for preparing the dispersant and softening agent of this invention uses conventional raw materials and mild reaction conditions, and the process is simple and easily industrialized. No special equipment is required, it is compatible with existing production lines, and significantly reduces the barriers to industrialization and costs.

[0046] In this invention, the solvent can be any solvent in the art that can dissolve the above four monomers well and is easy to remove subsequently, preferably one or more selected from N-methylpyrrolidone, dimethylformamide and ethyl acetate.

[0047] In this invention, the phosphate groups in the phosphate ester monomer molecules can form a strong interaction with the surface of the lithium iron phosphate cathode material, effectively preventing particle agglomeration and improving the dispersion effect. Specifically, they can be selected from one or more of phosphate methacrylate, phosphate ethyl acrylate, and allyl dihydrophosphate.

[0048] In this invention, the amine group in the amine monomer can regulate the interfacial charge distribution of the slurry, enhance the viscosity stability of the slurry, and facilitate uniform coating in the subsequent process. Specifically, it can be selected from one or more of diethanolamine acrylate, N-methyldiethanolamine methacrylate and aminoethyl methacrylate.

[0049] In this invention, the amide bond in the amide monomer can enhance the polarity and compatibility of the molecular chain, improve the filterability of the slurry, thereby accelerating the production speed of the electrode and improving production efficiency. Specifically, it can be selected from one or more of acrylamide, methacrylamide and N-methacrylamide.

[0050] In this invention, the flexible segments of the ether bonds in the ether monomer can improve the flexibility of the electrode, reduce the elongation of the electrode, and effectively avoid cracking and powder shedding during electrode processing (rolling, cutting) and use; and reduce structural damage to the electrode caused by volume changes during battery cycling, thereby improving battery cycle stability and safety. Specifically, it can be selected from one or more of polyethylene glycol monomethyl ether acrylate, polyethylene glycol monoethyl ether methacrylate, and polypropylene glycol monomethyl ether acrylate.

[0051] In this invention, the molar ratio of the phosphate ester monomers, amine monomers, amide monomers, and ether monomers is 20~35:15~25:10~20:25~40. This ratio range ensures the synergistic effect of each functional group, achieving the best dispersion and flexibility effect. The proportion of phosphate ester monomers in this invention maintains the flexibility of the electrode while preventing slurry agglomeration; the proportion of ether monomers in this invention ensures good dispersion stability of the slurry while guaranteeing the flexibility of the electrode.

[0052] In this invention, the initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile and benzoyl peroxide, and the amount of initiator added is 0.5 to 2% of the total mass of the four monomers.

[0053] In this invention, the inert atmosphere, in order to isolate oxygen and ensure the smooth progress of the reaction, can be a nitrogen atmosphere and / or an argon atmosphere.

[0054] In this invention, the conditions for the polymerization reaction include: a temperature of 60~80℃, a stirring rate of 200~400rpm, and a time of 4~8h. This temperature and time range can ensure that the monomers are fully polymerized to form a polymer with a suitable molecular weight.

[0055] In this invention, the prepolymerization method includes: mixing monomers that serve as the backbone in the presence of a solvent, and carrying out a prepolymerization reaction at a temperature of 40-60°C, a stirring rate of 100-200 rpm, and a time of 1-2 h.

[0056] In this invention, after the polymerization reaction, the solvent needs to be removed by vacuum distillation. The conditions for removing the solvent by vacuum distillation can be carried out according to conventional conditions in the art.

[0057] Thirdly, the present invention provides an application of the dispersant and softening agent as described in the present invention in the positive electrode of a lithium iron phosphate battery, wherein the amount of the dispersant and softening agent added is 0.05 to 0.5% of the mass of the positive electrode active material, lithium iron phosphate.

[0058] Fourthly, the present invention provides a lithium iron phosphate battery positive electrode slurry, wherein the lithium iron phosphate battery positive electrode slurry is composed of the following components in mass fractions: 90-98% lithium iron phosphate, 0.1-2% conductive agent, 1.2-2.4% binder, and 0.05-0.5% dispersant and softener; The dispersing and softening agent is the dispersing and softening agent described in this invention.

[0059] In this invention, the solid content of the lithium iron phosphate battery cathode slurry is 55-70%.

[0060] In this invention, the conductive agent is selected from one or more of acetylene black, Ketjen black, and carbon nanotubes.

[0061] In this invention, the adhesive is polyvinylidene fluoride and / or polytetrafluoroethylene.

[0062] In this invention, the solvent for the lithium iron phosphate battery cathode slurry is N-methylpyrrolidone.

[0063] Fifthly, the present invention provides a positive electrode sheet for a lithium iron phosphate battery, wherein the positive electrode sheet is prepared from the positive electrode slurry of the lithium iron phosphate battery described in the present invention; The bending radius of the positive electrode sheet of the lithium iron phosphate battery is ≤6mm, and the elongation is ≤1%.

[0064] The present invention will be described in detail below through examples.

[0065] Example 1 (4 monomers, main chain ethylene carbon chain, monomers are branched chains) 1. Design and molecular structure of dispersants and softeners: Monomer composition and molar ratio: Phosphate methacrylate (P): Diethanolamine acrylate (A): Acrylamide (Am): Polyethylene glycol monomethyl ether acrylate (E, m=5) = 25:20:15:40; Structural design: The main chain is a -CH2-CH2-ethylene carbon chain, and the four monomers are connected as independent side chains through ester bonds / amide bonds.

[0066] Molecular structural formula: -[CH2-CH2] k -, The side chains are: -OOC-CH(CH3)-PO(OH)2 (P-branch); -OOC-CH2-N(CH2CH2OH)2 (A-branch); -NH-CO-CH2- (Am branched); -OOC-CH2-O-(CH2CH2O)5-CH3 (E-branch) (k=100).

[0067] 2. Preparation of dispersing and softening agents: According to the above molar ratio, 25 mmol of phosphate methacrylate, 20 mmol of diethanolamine acrylate, 15 mmol of acrylamide, and 40 mmol of polyethylene glycol monomethyl ether acrylate were added to a three-necked flask. 50 mL of N-methylpyrrolidone and 1.2 g of azobisisobutyronitrile (1% of the total mass of the four monomers) were added. Nitrogen gas was purged into the flask to replace the air three times. The reaction system was heated to 70 °C and stirred at a constant temperature for 6 h. After the reaction was completed, the solvent was removed by vacuum distillation at 55 °C and 0.07 MPa to obtain dispersant softener A1.

[0068] 3. Preparation of positive electrode slurry and electrode sheet: By mass fraction, 96.9% lithium iron phosphate, 0.8% acetylene black, 2% polyvinylidene fluoride, and 0.3% dispersant and softener A1 were mixed. Using N-methylpyrrolidone (NMP) as solvent, the solid content of the slurry was controlled at 70%, with a mass fraction of NMP:solid content = 30:70. The solvent was added to a mixing tank and stirred at a high speed of 800~1500 r / min to disperse the slurry evenly. The viscosity of the slurry was tested, and by adding NMP, the viscosity was adjusted to 10000 mPa·s. Then, it was slowly stirred at 600 r / min for 20 min. The solid content was tested before shipment to obtain the positive electrode slurry. This positive electrode slurry was coated onto the surface of an aluminum foil current collector, dried at 90℃ for 3 h, and then rolled under 15 MPa pressure to obtain the positive electrode sheet A1.

[0069] Example 2 (4 monomers, the main chain is a monomer copolymer chain, and some monomers are polymerized into side chains) 1. Design and molecular structure of dispersants and softeners: Monomer composition and molar ratio: Phosphate methacrylate (P): Diethanolamine acrylate (A): Acrylamide (Am): Polyethylene glycol monomethyl ether acrylate (E, m=5) = 20:25:10:45; Structural design: The main chain is a copolymer of P and A (-PO(OH)2-CH2-CH2-N(CH2CH2OH)2-), and Am and E are polymerized into side chains attached to the methylene group of the main chain.

[0070] Molecular structural formula: -[PO(OH)2-CH2-CH2-N(CH2CH2OH)2-CH2] k -, The side chain is: -NH-CO-CH2-O-(CH2CH2O)5-CH3 (Am-E copolymer side chain) (k=90).

[0071] 2. Preparation of dispersing and softening agents: First, 20 mmol of phosphate methacrylate and 25 mmol of diethanolamine acrylate were added to a three-necked flask, followed by 30 mL of N-methylpyrrolidone. The mixture was heated to 60 °C for prepolymerization for 2 h. Then, 10 mmol of acrylamide, 45 mmol of polyethylene glycol monomethyl ether acrylate, and 1.3 g of azobisisobutyronitrile were added. Nitrogen gas was introduced to purge the mixture three times, and the mixture was heated to 70 °C for 5 h. After the reaction was completed, the solvent was removed by vacuum distillation at 55 °C and 0.07 MPa to obtain dispersant softener A2.

[0072] 3. Preparation of positive electrode slurry and electrode sheet: The preparation process of the positive electrode slurry and electrode sheet in Example 1 was carried out, except that "dispersant and flexible agent A1" was replaced with "dispersant and flexible agent A2" while other conditions remained unchanged, and positive electrode sheet A2 was obtained.

[0073] Example 3 (4 monomers, P dosage gradient 1: P=30) The method of Example 1 was carried out, except that the monomer combination and molar ratio were phosphate methacrylate (P): diethanolamine acrylate (A): acrylamide (Am): polyethylene glycol monomethyl ether acrylate (E, m=5) = 30:18:17:35, and other conditions remained unchanged, resulting in positive electrode A3.

[0074] Example 4 (4 monomers, P dosage gradient 2: P=35) The method of Example 1 was carried out, except that the monomer combination and molar ratio were phosphate methacrylate (P): diethanolamine acrylate (A): acrylamide (Am): polyethylene glycol monomethyl ether acrylate (E, m=5) = 35:15:10:40, and other conditions remained unchanged, resulting in positive electrode A4.

[0075] Example 5 (4 monomers, E dosage gradient 1: E=30) The method of Example 1 was implemented, except that the monomer combination and molar ratio were phosphate methacrylate (P): diethanolamine acrylate (A): acrylamide (Am): polyethylene glycol monomethyl ether acrylate (E, m=5) = 25:22:23:30, and other conditions remained unchanged, resulting in positive electrode A5.

[0076] Example 6 (4 monomers, E dosage gradient 2: E=45) The method of Example 1 was implemented, except that the monomer combination and molar ratio were phosphate methacrylate (P): diethanolamine acrylate (A): acrylamide (Am): polyethylene glycol monomethyl ether acrylate (E, m=5) = 22:18:15:45, and other conditions remained unchanged, resulting in positive electrode A6.

[0077] Example 7 (4 monomers, Am dosage gradient 1: Am=20) The method of Example 1 was implemented, except that the monomer combination and molar ratio were phosphate methacrylate (P): diethanolamine acrylate (A): acrylamide (Am): polyethylene glycol monomethyl ether acrylate (E, m=5) = 24:19:20:37, and other conditions remained unchanged, resulting in positive electrode A7.

[0078] Example 8 (4 monomers, Am dosage gradient 2: Am=12) The method of Example 1 was implemented, except that the monomer combination and molar ratio were phosphate methacrylate (P): diethanolamine acrylate (A): acrylamide (Am): polyethylene glycol monomethyl ether acrylate (E, m=5) = 27:21:12:40, and other conditions remained unchanged, resulting in positive electrode A8.

[0079] Example 9 (4 monomers, A dosage gradient 1: A=23) The method of Example 1 was implemented, except that the monomer combination and molar ratio were phosphate methacrylate (P): diethanolamine acrylate (A): acrylamide (Am): polyethylene glycol monomethyl ether acrylate (E, m=5) = 25:23:16:36, and other conditions remained unchanged, resulting in positive electrode A9.

[0080] Example 10 (4 monomers, A dosage gradient 2: A=16) The method of Example 1 was implemented, except that the monomer combination and molar ratio were phosphate methacrylate (P): diethanolamine acrylate (A): acrylamide (Am): polyethylene glycol monomethyl ether acrylate (E, m=5) = 26:16:17:41, and other conditions remained unchanged, resulting in positive electrode A10.

[0081] Example 11 (4 monomers, main chain is PA copolymer chain, Am-E copolymer is side chain) 1. Design and molecular structure of dispersants and softeners: Monomer composition and molar ratio: Phosphate methacrylate (P) 25: Diethanolamine acrylate (A) 20: Acrylamide (Am) 15: Polyethylene glycol monomethyl ether acrylate (E, m=5) = 25:20:15:40; Structural design: The main chain is an alternating PA copolymer chain, and Am and E copolymers form side chains that are connected to the nitrogen atoms of the main chain.

[0082] Molecular structural formula: -[PO(OH)2-CH2-CH2-N(CH2CH2OH)2-CH2] k -, The side chain is: -CH2-NH-CO-CH2-O-(CH2CH2O)5-CH3 (Am-E copolymer side chain) (k=100) 2. Preparation of dispersing and softening agents: First, 25 mmol of phosphate methacrylate and 20 mmol of diethanolamine acrylate were added to a three-necked flask, followed by 30 mL of N-methylpyrrolidone. The mixture was heated to 60 °C for prepolymerization for 2 h. Then, 15 mmol of acrylamide, 40 mmol of polyethylene glycol monomethyl ether acrylate, and 1.3 g of azobisisobutyronitrile were added. Nitrogen gas was introduced to purge the mixture three times, and the mixture was heated to 70 °C for 5 h. After the reaction was completed, the solvent was removed by vacuum distillation at 55 °C and 0.07 MPa to obtain the dispersant softener A11.

[0083] 3. Preparation of positive electrode slurry and electrode sheet: The preparation process of the positive electrode slurry and electrode sheet in Example 1 was carried out, except that "dispersant flexible agent A1" was replaced with "dispersant flexible agent A11", while other conditions remained unchanged, and positive electrode sheet A11 was obtained.

[0084] Comparative Example 1 (3 monomers, P+A+E) 1. Design and molecular structure of dispersants and softeners: Monomer composition and molar ratio: Phosphate methacrylate (P): Diethanolamine acrylate (A): Polyethylene glycol monomethyl ether acrylate (E, m=5) = 28:22:50; Structural design: The main chain is a copolymer of P and A, and E is an independent side chain.

[0085] Molecular structural formula: -[PO(OH)2-CH2-CH2-N(CH2CH2OH)2-] k - The side chain is: -OOC-CH2-O-(CH2CH2O)5-CH3 (E-branch) (k=95) 2. Preparation of dispersing and softening agents: According to the above molar ratio, 28 mmol of phosphate methacrylate, 22 mmol of diethanolamine acrylate, and 50 mmol of polyethylene glycol monomethyl ether acrylate were added to a three-necked flask, along with 45 mL of N-methylpyrrolidone as solvent and 1.1 g of azobisisobutyronitrile as initiator. Nitrogen gas was purged into the flask to replace the air three times. The reaction system was heated to 70 °C and stirred at a constant temperature for 6 h. After the reaction was completed, the solvent was removed by vacuum distillation at 55 °C and 0.07 MPa to obtain the dispersant and softening agent D1.

[0086] 3. Preparation of positive electrode slurry and electrode sheet: The preparation process of the positive electrode slurry and electrode sheet in Example 1 was carried out, except that "dispersant and flexible agent A1" was replaced with "dispersant and flexible agent D1" while other conditions remained unchanged, and positive electrode sheet D1 was obtained.

[0087] Comparative Example 2 (3 monomers, P+Am+E) 1. Design and molecular structure of dispersants and softeners: Monomer composition and molar ratio: Phosphate methacrylate (P): Acrylamide (Am): Polyethylene glycol monomethyl ether acrylate (E, m=5) = 26:20:54; Structural design: The main chain is a -CH2-CH2-ethylene carbon chain, and the four monomers are connected as independent side chains through ester bonds / amide bonds.

[0088] Molecular structural formula: -[CH2-CH2] k -, The side chains are: -OOC-CH(CH3)-PO(OH)2 (P-branch); -OOC-CH2-N(CH2CH2OH)2 (A-branch); -NH-CO-CH2- (Am branched); -OOC-CH2-O-(CH2CH2O)5-CH3 (E-branch) (k=100).

[0089] 2. Preparation of dispersing and softening agents: According to the above molar ratio, 26 mmol of phosphate methacrylate, 20 mmol of acrylamide, and 54 mmol of polyethylene glycol monomethyl ether acrylate were added to a three-necked flask, along with 50 mL of N-methylpyrrolidone and 1.2 g of azobisisobutyronitrile (1% of the total mass of the four monomers). Nitrogen gas was introduced to purge the air from the flask three times. The reaction system was heated to 70 °C and stirred at a constant temperature for 6 h. After the reaction was completed, the solvent was removed by vacuum distillation at 55 °C and 0.07 MPa to obtain the dispersant softener D2.

[0090] 3. Preparation of positive electrode slurry and electrode sheet: The preparation process of the positive electrode slurry and electrode sheet in Example 1 was carried out, except that "dispersant and flexible agent A1" was replaced with "dispersant and flexible agent D2" while other conditions remained unchanged, and positive electrode sheet D2 was obtained.

[0091] Comparative Example 3 (3 monomers, A+Am+E) 1. Design and molecular structure of dispersants and softeners: Monomer composition and molar ratio: Diethanolamine acrylate (A): Acrylamide (Am): Polyethylene glycol monomethyl ether acrylate (E, m=5) = 24:21:55; Structural design: The main chain is a copolymer of A and Am, and E is an independent side chain.

[0092] Molecular structural formula: -[N(CH2CH2OH)2-CH2-CH2-NH-CO-CH2] k - The side chain is an E-branch (k=95). 2. Preparation of dispersing and softening agents: According to the above molar ratio, 24 mmol of diethanolamine acrylate, 21 mmol of acrylamide, and 55 mmol of polyethylene glycol monomethyl ether acrylate were added to a three-necked flask, along with 50 mL of N-methylpyrrolidone and 1.2 g of azobisisobutyronitrile (1% of the total mass of the four monomers). Nitrogen gas was introduced to purge the air from the flask three times. The reaction system was heated to 70 °C and stirred at a constant temperature for 6 h. After the reaction was completed, the solvent was removed by vacuum distillation at 55 °C and 0.07 MPa to obtain the dispersant softener D3.

[0093] 3. Preparation of positive electrode slurry and electrode sheet: The preparation process of the positive electrode slurry and electrode sheet in Example 1 was carried out, except that "dispersant and flexible agent A1" was replaced with "dispersant and flexible agent D3" while other conditions remained unchanged, and positive electrode sheet D3 was obtained.

[0094] Comparative Example 4 (2 monomers, P+E) 1. Design and molecular structure of dispersants and softeners: Monomer composition and molar ratio: Phosphate methacrylate (P): Polyethylene glycol monomethyl ether acrylate (E, m=5) = 32:68; Structural design: The main chain is a copolymer chain of alternating P and E.

[0095] Molecular structural formula: -[PO(OH)2-CH2-CH2-O-(CH2CH2O)5-CH3] k - (k=105) 2. Preparation of dispersing and softening agents: According to the above molar ratio, 32 mmol of phosphate methacrylate and 68 mmol of polyethylene glycol monomethyl ether acrylate were added to a three-necked flask, along with 40 mL of N-methylpyrrolidone and 1 g of azobisisobutyronitrile. Nitrogen gas was purged into the flask to replace the air three times. The reaction system was heated to 70 °C and stirred at a constant temperature for 6 h. After the reaction was completed, the solvent was removed by vacuum distillation at 55 °C and 0.07 MPa to obtain the dispersant softener D4.

[0096] 3. Preparation of positive electrode slurry and electrode sheet: The preparation process of the positive electrode slurry and electrode sheet in Example 1 was carried out, except that "dispersant and flexible agent A1" was replaced with "dispersant and flexible agent D4" while other conditions remained unchanged, and positive electrode sheet D4 was obtained.

[0097] Comparative Example 5 (2 monomers, A + Am) 1. Design and molecular structure of dispersants and softeners: Monomer composition and molar ratio: Diethanolamine acrylate (A): Acrylamide (Am) = 45:55; Structural design: The main chain is an alternating copolymer of A and Am.

[0098] Molecular structural formula: -[N(CH2CH2OH)2-CH2-CH2-NH-CO-CH2] k -(k=110) 2. Preparation of dispersing and softening agents: Using the same preparation process as Comparative Example 4, dispersant and softener D5 was obtained.

[0099] 3. Preparation of positive electrode slurry and electrode sheet: Using the same process as in Example 1, but replacing "dispersant flexible agent A1" with "dispersant flexible agent D5" while keeping other conditions unchanged, positive electrode sheet D5 is obtained.

[0100] Comparative Example 6 (2 monomers, Am+E) 1. Design and molecular structure of dispersants and softeners: Monomer composition and molar ratio: Acrylamide (Am): Polyethylene glycol monomethyl ether acrylate (E, m=5) = 30:70; Structural design: The main chain is an alternating copolymer of Am and E.

[0101] Molecular structural formula: -[NH-CO-CH2-CH2-O-(CH2CH2O)5-CH3] k -(k=100) 2. Preparation of dispersing and softening agents: According to the above molar ratio, 30 mmol of acrylamide and 70 mmol of polyethylene glycol monomethyl ether acrylate were added to a three-necked flask, along with 40 mL of N-methylpyrrolidone and 1 g of azobisisobutyronitrile. Nitrogen gas was purged into the flask to replace the air three times. The reaction system was heated to 70 °C and stirred at a constant temperature for 6 h. After the reaction was completed, the solvent was removed by vacuum distillation at 55 °C and 0.07 MPa to obtain the dispersant softener D6.

[0102] 3. Preparation of positive electrode slurry and electrode sheet: The preparation process of the positive electrode slurry and electrode sheet in Example 1 was carried out, except that "dispersant and flexible agent A1" was replaced with "dispersant and flexible agent D6" while other conditions remained unchanged, and positive electrode sheet D6 was obtained.

[0103] Comparative Example 7 (4 monomers, main chain is Am-E copolymer chain, PA copolymer is side chain) 1. Design and molecular structure of dispersants and softeners: Monomer composition and molar ratio: Phosphate methacrylate (P): Diethanolamine acrylate (A): Acrylamide (Am): Polyethylene glycol monomethyl ether acrylate (E, m=5) = 25:20:15:40; Structural design: The main chain is an alternating Am-E copolymer chain, and P copolymerizes with A to form side chains that connect to the amide nitrogen atoms of the main chain.

[0104] Molecular structural formula: -[-NH-CO-CH2-CH2-O-(CH2CH2O)5-CH3] k -, The side chain is: -CH2-N(CH2CH2OH)2-CH2-PO(OH)2 (PA copolymer side chain) (k=100) 2. Preparation of dispersing and softening agents: First, 15 mmol of acrylamide and 40 mmol of polyethylene glycol monomethyl ether acrylate were added to a three-necked flask, followed by 30 mL of N-methylpyrrolidone. The mixture was heated to 60 °C for prepolymerization for 2 h. Then, 25 mmol of phosphate methacrylate (P), 20 mmol of diethanolamine acrylate, and 1.3 g of azobisisobutyronitrile were added. Nitrogen gas was introduced to purge the mixture three times, and the mixture was heated to 70 °C for 4 h. After the reaction was completed, the solvent was removed by vacuum distillation at 55 °C and 0.07 MPa to obtain the dispersant and softening agent D7.

[0105] 3. Preparation of positive electrode slurry and electrode sheet: The preparation process of the positive electrode slurry and electrode sheet in Example 1 was carried out, except that "dispersant and flexible agent A1" was replaced with "dispersant and flexible agent D7" while other conditions remained unchanged, and positive electrode sheet D7 was obtained.

[0106] Test Example 1: The positive electrode slurry and electrode sheet prepared in Examples 1-11 and Comparative Examples 1-7 were tested for performance. The results are shown in Table 1.

[0107] Example Sample Testing: Solid content of slurry: Take a certain mass of slurry and measure its weight as m1. Place it on the measuring instrument. After the solvent in the slurry evaporates to the point where the index of the measuring instrument no longer changes, measure its remaining weight as m2. Then the solid content of the slurry is m2 / m1×100%.

[0108] 48-hour viscosity change rate: Take a 500mL beaker and slowly pour the prepared positive electrode slurry into it until the liquid level reaches 400mL. Use a viscometer to measure its initial viscosity and record it as P0. Then seal it with plastic film to avoid excessive solvent evaporation and prolonged contact with air, which could lead to deterioration of the slurry properties. After standing at room temperature (25℃) in the dark for 48 hours, use a viscometer to measure the viscosity of the slurry after standing and record it as P1. Record the result of P1 / P0 as the 48-hour viscosity change rate.

[0109] Filtration speed: for an area of ​​50×50cm 2 Take a 150-mesh filter screen and fold it into a funnel shape. Then take two beakers; place 500 mL of the slurry described in the example in one beaker, and place the funnel-shaped filter screen at the mouth of the other beaker. Pour the 500 mL slurry through the funnel into the other beaker, and record the time required for the filtered slurry to reach 300 mL. Divide 300 by the time taken to calculate the filtration rate.

[0110] Electrode bending radius: Cut the electrode into a strip of 5cm×10cm. Bend the two ends of the strip together along its length. The central area of ​​the electrode will be bent into an arc. Measure the radius of this arc area with a soft ruler and record it as the electrode bending radius.

[0111] Electrode elongation: The electrode was cut into strips of 5cm × 100cm and passed through a cold-pressing roller along its length. The pressure was the actual test pressure in the example. After cold pressing, the length of the electrode was recorded as L1. The elongation of the electrode is calculated as L1 - 100 / 100.

[0112] Table 1

[0113] As shown in Table 1, the positive electrode slurry and positive electrode sheet of the lithium iron phosphate battery prepared using the dispersant and flexibility agent A1 obtained in Example 1 exhibit balanced overall performance. The core reason is that the proportions of the four monomers are moderate, and they are distributed in the main chain in the form of independent branches, allowing each functional group to play its full role: the phosphate ester groups of the P branch form a strong interaction with lithium iron phosphate to ensure dispersibility; the amine groups of the A branch regulate the interfacial charge to ensure viscosity stability; the amide bonds of the Am branch improve compatibility to ensure filterability; and the ether bonds of the E branch provide flexibility to ensure the flexibility of the electrode sheet, with no obvious functional group shortcomings.

[0114] The performance of the positive electrode slurry and positive electrode sheet of the lithium iron phosphate battery prepared using the dispersant and softener of Example 2 was slightly inferior to that of Example 1. This is because, in terms of structural design, the Am and E copolymers form a single branch, which limits the range of action of the amide and ether bonds. Furthermore, the proportion of Am monomer is only 10%, lower than the 15% in Example 1, resulting in a slight decrease in compatibility and a reduced filtration speed. Simultaneously, the main chain is a PA copolymer chain, which, compared to the ethylene main chain of Example 1, has slightly fewer interaction sites between the phosphate ester groups and the positive electrode material, leading to slightly lower solids content and viscosity stability.

[0115] The positive electrode slurry and positive electrode sheet of the lithium iron phosphate battery prepared using the dispersant and flexibility agent of Example 3 exhibit the best overall performance. The core reason is that the proportion of P monomers is increased to 30%, higher than 25% in Example 1, meaning that more phosphate ester groups form strong interactions with the lithium iron phosphate surface, effectively inhibiting particle agglomeration, increasing solid content, and enhancing viscosity stability. At the same time, the proportion of Am monomers is increased to 17%, increasing the number of amide bonds, further optimizing compatibility, and improving filtration speed. The proportion of E monomers at 35% still ensures sufficient flexible segments, with only the electrode bending radius being slightly larger than that of the example with a higher E proportion, and there are no obvious performance shortcomings.

[0116] The lithium iron phosphate battery cathode slurry prepared using the dispersant and softener of Example 4 exhibited the best dispersion-related performance, but the cathode electrode flexibility decreased. This was because the proportion of P monomer was too high (35%). While this significantly improved dispersibility and viscosity stability, it resulted in a relatively insufficient proportion of A, Am, and E monomers: A monomer at 15% (minimum value) slightly reduced the interfacial charge regulation capability; Am monomer at 10% (minimum value) led to reduced compatibility and decreased filtration speed; more importantly, although the proportion of E monomer at 40% was not low, the excessive P monomer increased the rigidity of the molecular chain, weakening the softening effect of the flexible segments, resulting in an increased electrode bending radius and elongation.

[0117] The positive electrode slurry for lithium iron phosphate batteries prepared using the dispersant and softener of Example 5 exhibits the best filterability, but the flexibility of the resulting positive electrode sheet is slightly reduced. This is because the proportion of Am monomer is increased to 23%, higher than the 10-20% specified in this invention. The large number of amide bonds significantly improves the compatibility between the molecules and the components of the slurry, reduces agglomerated particles, and achieves the highest filtration rate. However, the proportion of E monomer decreases to 30% (the lowest value), resulting in insufficient flexible segments and a larger bending radius of the electrode sheet compared to examples with higher E proportions. Meanwhile, the 25% P monomer content is at a conventional level, resulting in average dispersibility and slightly lower solids content. Although the 22% A monomer content can regulate charge, its viscosity stability is slightly poor due to the influence of the phosphate ester group and ether bond ratio.

[0118] The positive electrode of the lithium iron phosphate battery prepared using the dispersant and flexibility agent of Example 6 exhibits the best flexibility. This is because the proportion of E monomer is increased to 45%, exceeding the range of 25-40% defined in this invention. A large number of flexible ether chain segments penetrate into the electrode interior, improving the flexibility of the electrode's microstructure, resulting in the smallest bending radius and lowest elongation. However, the excessively high proportion of E monomer leads to a relatively insufficient proportion of P monomer and Am monomer: 22% P monomer slightly reduces dispersibility and results in a moderate solids content; while 15% Am monomer is within the range defined in this invention, the steric hindrance of the E chain segments slightly weakens the interaction between the amide bonds and the slurry components, leading to a decrease in filtration speed.

[0119] The positive electrode slurry for lithium iron phosphate batteries prepared using the dispersant and softener of Example 7 exhibits excellent filtration properties, but the flexibility of the positive electrode sheet is slightly reduced. This is because the proportion of Am monomer is increased to 20%, resulting in a sufficient number of amide bonds and excellent compatibility among the components in the positive electrode slurry, thus allowing the filtration speed of the slurry to approach the highest value of Example 5. However, the increased proportion of Am monomer leads to a decrease in the proportion of E monomer to 37%, resulting in slightly fewer flexible segments in the dispersant and softener, and a slightly larger bending radius of the prepared positive electrode sheet. The appropriate proportions of P monomer and A monomer ensure the dispersibility and viscosity stability of the components in the prepared positive electrode slurry, resulting in a balanced and superior overall performance.

[0120] The positive electrode slurry and positive electrode sheet of the lithium iron phosphate battery prepared using the dispersant and softener of Example 8 exhibit balanced overall performance, but the filterability of the positive electrode slurry is slightly reduced. This is because the proportion of Am monomer is reduced to 12%, the number of amide bonds decreases, and the compatibility of the components in the positive electrode slurry is slightly reduced, resulting in a lower filtration rate than in the example with a higher proportion of Am monomer. However, the proportion of P monomer (27%) improves the dispersibility of the components in the positive electrode slurry, the proportion of A monomer (21%) ensures the viscosity stability of the positive electrode slurry, and the proportion of E monomer (40%) ensures the flexibility of the positive electrode sheet, resulting in no significant shortcomings in any of its properties. Only the filterability of the positive electrode slurry is slightly worse due to the insufficient Am monomer.

[0121] The positive electrode slurry for lithium iron phosphate batteries prepared using the dispersant and flexibility agent of Example 9 exhibits excellent viscosity stability, but the flexibility of the positive electrode sheet decreases slightly. This is because the proportion of monomer A is increased to 23%, resulting in a sufficient number of amine groups, which can more effectively regulate the interfacial charge distribution of the slurry and achieve a lower viscosity change rate. However, the increased proportion of monomer A leads to a decrease in the proportion of monomer E to 36%, resulting in slightly fewer flexible segments and a slightly larger bending radius of the electrode sheet. The appropriate proportions of monomer P and monomer Am ensure the dispersibility and basic compatibility of each component in the positive electrode slurry, resulting in a balanced and superior overall performance.

[0122] The lithium iron phosphate battery cathode slurry and cathode sheet prepared using the dispersant and flexibility agent of Example 10 exhibit balanced overall performance, but the viscosity stability of the cathode slurry is slightly reduced. This is because the proportion of monomer A is reduced to 16%, resulting in a decrease in the number of amine groups and a slight decrease in the interfacial charge regulation capability. Consequently, the viscosity change rate of the cathode slurry is slightly higher than in the example with a higher proportion of monomer A. However, the proportion of monomer E increases to 41%, providing sufficient flexible segments and resulting in a more flexible cathode sheet. Monomer P at 26% improves dispersibility, while monomer Am at 17% ensures the compatibility of the components in the cathode slurry, leading to a higher filtration rate and a more balanced overall performance.

[0123] The positive electrode slurry and positive electrode sheet of the lithium iron phosphate battery prepared using the dispersant and softener of Example 11 exhibit balanced overall performance, but are slightly inferior to those of Example 1. This is because, in terms of structural design, the main chain is a PA copolymer chain, and the Am-E copolymer is a branch chain. Although the proportions of the four monomers are the same as in Example 1, the copolymer branch chain limits the functional groups of Am and E: the contact opportunities between the amide bonds and the slurry components are reduced, resulting in a slight decrease in filtration speed; the flexibility of the ether bonds is slightly weakened, leading to a slightly larger bending radius; the PA main chain ensures the basic dispersibility and viscosity stability of each component in the positive electrode slurry, thus the overall performance is still relatively balanced, but not as good as the independently branched structure.

[0124] The positive electrode of the lithium iron phosphate battery prepared using the dispersant and softener of Comparative Example 1 exhibits good flexibility but poor filtration. The core reason is the lack of amide monomers (no amide bonds), and amide bonds are key functional groups for improving compatibility. This leads to a significant decrease in the compatibility between the molecules and the components of the slurry, an increase in agglomerated particles, and a substantial reduction in filtration speed. At the same time, due to the absence of Am monomers, the synergistic effect of interfacial charge regulation is weakened, resulting in slightly poor viscosity stability. However, the E monomer ratio is as high as 50%, providing excellent flexibility, and the P and A monomer ratios are moderate, ensuring basic dispersibility.

[0125] The lithium iron phosphate battery cathode slurry prepared using the dispersant and softener of Comparative Example 2 exhibits good filterability but poor viscosity stability, while the cathode sheet demonstrates good flexibility. This is because it lacks amine monomers (no amine groups). Amine groups are key functional groups for regulating the interfacial charge distribution and stabilizing viscosity in the slurry; their absence leads to an imbalance in the interfacial charge, resulting in a significant increase in viscosity change rate after 48 hours. However, the appropriate proportions of P, Am, and E monomers ensure good dispersibility of the components in the cathode slurry, while Am monomers ensure compatibility, resulting in high filtration speed. E monomers also contribute to the good flexibility of the prepared cathode sheet, thus contributing to its other good properties.

[0126] The lithium iron phosphate battery cathode sheet prepared using the dispersant and flexibility enhancer of Comparative Example 3 exhibits the best flexibility, but the cathode slurry has poor dispersibility. This is because it lacks phosphate ester monomers (no phosphate ester groups). Phosphate ester groups are key functional groups that interact with lithium iron phosphate and improve dispersibility; their absence prevents effective inhibition of particle agglomeration, resulting in a significant reduction in solid content. Monomers A and Am ensure basic viscosity stability and compatibility of the cathode slurry, while the high proportion of monomer E (55%) results in the best flexibility of the cathode sheet. However, the insufficient core dispersibility of the cathode slurry limits the overall performance.

[0127] The positive electrode slurry and positive electrode sheet of the lithium iron phosphate battery prepared using the dispersant and flexibility agent of Comparative Example 4 exhibited poor performance in multiple aspects. This is because it contains only P and E monomers, lacking amine groups to regulate charge and amide bonds to improve the compatibility between components in the positive electrode slurry. This results in extremely poor viscosity stability and poor filterability of the positive electrode slurry. Although the 32% proportion of P monomers ensured basic dispersibility of the positive electrode slurry and the 68% proportion of E monomers ensured flexibility of the positive electrode sheet, the absence of the two core functional groups, amine groups and amide bonds, significantly reduced the overall performance.

[0128] The lithium iron phosphate battery cathode slurry and cathode sheet prepared using the dispersant and flexible agent of Comparative Example 5 exhibited the worst overall performance. This is because it contains only A and Am monomers, lacking phosphate ester groups and ether bonds. The absence of P monomers results in extremely poor dispersibility and the lowest solids content in the cathode slurry; the absence of E monomers leads to strong molecular chain rigidity in the dispersant and flexible agent, resulting in extremely poor flexibility in the prepared cathode sheet, i.e., the largest bending radius and the highest elongation. Although A and Am monomers ensured basic viscosity stability and compatibility of the components in the cathode slurry, the dispersibility and solids content of the prepared cathode slurry, as well as the flexibility of the cathode sheet, failed to meet application requirements.

[0129] The lithium iron phosphate battery cathode slurry prepared using the dispersant and softener of Comparative Example 6 exhibits the best filterability and cathode electrode flexibility, but its viscosity stability is extremely poor. This is because it contains only Am and E monomers, lacking phosphate ester and amine groups. The absence of A monomers prevents interfacial charge adjustment, resulting in the highest viscosity change rate of the cathode slurry. The absence of P monomers leads to generally poor dispersibility of the components in the cathode slurry and a low solids content. However, the 30% Am monomer content ensures excellent compatibility, resulting in the highest filtration rate, while the 70% E monomer content ensures excellent cathode electrode flexibility, exhibiting a "polarized" performance characteristic.

[0130] The overall performance of the positive electrode slurry and positive electrode sheet of the lithium iron phosphate battery prepared using the dispersant and softener of Comparative Example 7 was slightly inferior to that of Examples 1 and 11. The core reason is that in terms of structural design, the main chain is an Am-E copolymer chain, and the PA copolymer is a branch chain. The interaction between PA and the positive electrode material is weakened, resulting in a slight decrease in the dispersibility of each component in the positive electrode slurry, with a solid content of only 64%. At the same time, the amine group regulation effect of the A monomer is limited, and the viscosity stability of the slurry is slightly worse (viscosity change rate of 400% in 48h). The steric hindrance of the main chain Am-E copolymer chain is relatively large, which affects the role of Am and E functional groups. The filtration speed of 17.0 mL / min and the electrode bending radius of 4.6 mm are both slightly inferior to those of Example 1, and the overall performance is average.

[0131] In summary, the positive electrode slurry and positive electrode sheet prepared with the dispersant and softener of Example 3 exhibit the best overall performance. The positive electrode slurry has a relatively high solid content of 67%, the lowest viscosity change rate after 48 hours (290%), and a relatively fast filtration speed of 18.8 mL / min. Simultaneously, the positive electrode sheet has a small bending radius of 4.3 mm and a low elongation of 0.4%. All core performance indicators are excellent, with no obvious shortcomings. The four monomers are complete and in reasonable proportions: a slight increase in P monomer improves dispersibility, an appropriate amount of Am monomer ensures filtration performance, and sufficient E monomer ensures flexibility. The independent branched structure allows for full contact and interaction of the functional groups, maximizing the synergistic effect.

[0132] The positive electrode slurry and positive electrode sheet prepared by the dispersant and softener in Example 1 are slightly inferior to those in Example 3 in terms of various performance indicators. However, the monomer ratio is easier to control industrially, the production difficulty is lower, and the overall performance is still significantly better than other examples and existing technologies. It is suitable for scenarios with high requirements for production processes.

[0133] In Comparative Examples 1-6, only 2-3 monomer combinations were used to prepare dispersants and flexible agents. Due to the lack of some functional groups, they all had obvious performance defects. For example, in Examples 5 and 6, the groups with an unbalanced ratio of 4 monomers would result in one performance being optimal but other performances declining. In Comparative Example 7, the group with an unreasonable main chain-branch design would weaken the interaction between key functional groups and cathode materials, reducing the dispersion effect.

[0134] Compared with the dispersant and softener prepared in Example 3, the dispersant and softener prepared in Comparative Example 1 not only had a higher viscosity change rate over 48 hours, but also a much lower solid content in the cathode slurry. The solid content of the cathode slurry in Example 3 was 67%, while that in Comparative Example 1 was 63%. This difference has a significant impact on actual production: the solid content difference at four points in the cathode slurry is significant. Example 3 used 33% NMP, while Comparative Example 1 used 37% NMP. This means that 37-33 / 33=12.1% more solvent was actually added, resulting in a 12% increase in coating and drying energy consumption, a 12% increase in NMP solvent consumption, a 12% decrease in production capacity, and a significant increase in cost.

[0135] In summary, this invention achieves multiple technological breakthroughs by copolymerizing four specific monomers to form a dispersant and softener containing multiple functional groups. The resulting cathode slurry exhibits significantly increased solid content, a 48-hour viscosity change rate ≤500%, and a filtration speed increase of over 30%, reducing solvent usage and ensuring storage stability. The resulting cathode sheet has a bending radius ≤6mm and an elongation ≤1%, with significantly optimized flexibility and dimensional stability, preventing cracking and damage during processing and use. The electrode component distribution is more uniform, internal resistance is reduced, and battery cycle stability and safety are improved. The dispersant and softener preparation process of this invention is mild, requiring only 0.05~0.5% addition when preparing lithium iron phosphate battery cathode slurry, making it compatible with existing industrial processes. It balances performance and cost, addressing the pain points of existing additives such as limited functionality and poor compatibility.

[0136] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0137] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0138] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A dispersant and softening agent for the positive electrode of a lithium iron phosphate battery, characterized in that, The dispersant and softening agent is polymerized from phosphate ester monomers, amine monomers, amide monomers and ether monomers; The general molecular structure of the dispersant and softening agent is shown in formula (I): ; Wherein, R¹ is H or a C1~C4 alkyl group; R² is a C1~C3 alkyl group or a C1~C3 amino-substituted alkyl group; R³ is H or a C1~C2 alkyl group; n is an integer from 1 to 5; m is an integer from 3 to 10; and k is an integer from 50 to 200.

2. The dispersant and softening agent according to claim 1, characterized in that, The phosphate ester monomers are selected from one or more of phosphate methacrylate, phosphate ethyl acrylate, and allyl dihydrophosphate. The amine monomer is selected from one or more of diethanolamine acrylate, N-methyldiethanolamine methacrylate and aminoethyl methacrylate; The amide monomer is selected from one or more of acrylamide, methacrylamide, and N-methacrylamide; The ether monomers are selected from one or more of polyethylene glycol monomethyl ether acrylate, polyethylene glycol monoethyl ether methacrylate, and polypropylene glycol monomethyl ether acrylate.

3. The dispersing and softening agent according to claim 1 or 2, characterized in that, The molar ratio of the phosphate ester monomers, amine monomers, amide monomers and ether monomers is 20~35:15~25:10~20:25~40.

4. A method for preparing the dispersing and softening agent as described in any one of claims 1-3, characterized in that, The preparation method includes: adding phosphate ester monomers, amine monomers, amide monomers and ether monomers in the presence of a solvent, adding an initiator, and carrying out a polymerization reaction under an inert atmosphere; Alternatively, in the presence of a solvent, the main chain backbone monomers are prepolymerized first, then the remaining branched monomers are added and mixed, an initiator is added, and the polymerization reaction is carried out under an inert atmosphere. The main chain backbone monomer is selected from two of the following: phosphate ester monomers, amine monomers, amide monomers, and ether monomers; The remaining branched monomers are monomers other than the main chain backbone monomers among phosphate ester monomers, amine monomers, amide monomers, and ether monomers.

5. The preparation method according to claim 4, characterized in that, The solvent is selected from one or more of N-methylpyrrolidone, dimethylformamide, and ethyl acetate; The phosphate ester monomers are selected from one or more of phosphate methacrylate, phosphate ethyl acrylate, and allyl dihydrophosphate. The amine monomer is selected from one or more of diethanolamine acrylate, N-methyldiethanolamine methacrylate and aminoethyl methacrylate; The amide monomer is selected from one or more of acrylamide, methacrylamide, and N-methacrylamide; The ether monomer is selected from one or more of polyethylene glycol monomethyl ether acrylate, polyethylene glycol monoethyl ether methacrylate and polypropylene glycol monomethyl ether acrylate; The initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptanenitrile, and benzoyl peroxide; The inert atmosphere is a nitrogen atmosphere and / or an argon atmosphere.

6. The preparation method according to claim 4 or 5, characterized in that, The molar ratio of the phosphate ester monomer, amine monomer, amide monomer and ether monomer is 20~35:15~25:10~20:25~40; The amount of the initiator added is 0.5 to 2% of the total mass of the four monomers: phosphate ester monomers, amine monomers, amide monomers, and ether monomers.

7. The preparation method according to any one of claims 4-6, characterized in that, The conditions for the polymerization reaction include: a temperature of 60~80℃, a stirring rate of 200~400rpm, and a time of 4~8h; The prepolymerization conditions include: a temperature of 40~60℃, a stirring rate of 100~200rpm, and a time of 1~2h.

8. The application of a dispersant and softening agent as described in any one of claims 1-3 in the positive electrode of a lithium iron phosphate battery, characterized in that, The amount of the dispersant and softener added is 0.05~0.5% of the mass of the positive electrode active material, lithium iron phosphate.

9. A lithium iron phosphate battery cathode slurry, characterized in that, The lithium iron phosphate battery cathode slurry consists of the following components in the following mass fractions: Composition: 90-98% lithium iron phosphate, 0.1-2% conductive agent, 1.2-2.4% binder, and 0.05-0.5% dispersant and softener; Wherein, the dispersing and softening agent is the dispersing and softening agent according to any one of claims 1-3; The solid content of the lithium iron phosphate battery cathode slurry is 55-70%; Preferably, the conductive agent is selected from one or more of acetylene black, Ketjen black, and carbon nanotubes; The adhesive is polyvinylidene fluoride and / or polytetrafluoroethylene; The solvent for the positive electrode slurry of the lithium iron phosphate battery is N-methylpyrrolidone.

10. A positive electrode sheet for a lithium iron phosphate battery, characterized in that, The positive electrode sheet of the lithium iron phosphate battery is prepared from the positive electrode slurry of the lithium iron phosphate battery as described in claim 9; The bending radius of the positive electrode sheet of the lithium iron phosphate battery is ≤6mm, and the elongation is ≤1%.

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